This invention relates to a reinforcing material suitable for use in the outer panel of an automotive vehicle.
From the standpoint of resource-conservation and energy-conservation, for example, in the automobile field, it is very desirable for vehicle body weight to be reduced. Attempts to achieve this by reducing the thickness of materials or the number of parts result in deterioration in strength. For example, in case of the doors for automobiles, such attempts have induced problems such as low strength at various points (particularly tensile strength), insufficiently rigid outer panels, and poor handling feeling in the opening and closing of the doors.
In order to solve such problems, it is necessary to develop a suitable way to reinforce such structures. Reinforcement with heavy metal sheet is contradictory to the purpose of vehicle weight reduction, and hence it has been proposed to reinforce the door outer panels entirely or partly with light resin sheet materials.
However, door structures reinforced with resin sheet materials as heretofore proposed have many defects. For instance, simply bonding thin resin sheet material to the back of a door outer panel is nearly useless for increasing the thickness of the door panel and achieves poor reinforcing effect. If the thickness of the resin sheet is increased, the weight will also be increased. If packing is used between the resin sheet material and the door outer panel to ensure sufficient thickness, the reinforcing member will conform poorly to the curved shape of the outer panel, or will have a complicated structure. Thus satisfactorily practical proposals have not yet been made.